1. Field of the Invention
This invention relates to a reversible unidirectional fluid flow pump and more particularly to such a pump commonly referred to as a gerotor pump and having means for ensuring continued unidirectional pumping upon reversal of the pump drive shaft.
2. Description of the Prior Art
Gear pumps such as the reversible pump described in U.S. Pat. No. 3,273,501 are commonly used to deliver lubricant to refrigerant compressors in a refrigeration system. As explained in U.S. Pat. No. 3,574,489, orbital gear-sets providing rolling contact between an outer internally toothed gear which has one more tooth than an inner externally-toothed gear in which gears mesh with their axes eccentric to one another are commercially available under the generic designation "gerotors". Pumps employing such gear sets for positive displacement of fluid caused by the rolling contact between the meshing and gear teeth are referred to as gerotor pumps.
In such gerotor pumps, the pump inlets and outlets are generally defined in face plates on opposing planar sides of the mating orbital gears, with the inlet generally diametrically opposed from the outlet. Thus, with the gears rotating in one direction, the pump inlet is adjacent the area where the gears are separating and the outlet is adjacent the area where the gears are converging. By reversing the direction of rotation of the gears, the pump outlet becomes the inlet and the pump inlet becomes the outlet.
However, in instances where reversibility of the direction of rotation of the pump is desired yet it is also necessary that the pump inlet and outlet do not reverse, as a lubricating system, the pump rotor (i.e., the outer, internally-toothed gear) has been disposed in an opening of a rotatable eccentric collar or ring member within the pump which can be rotated through a 180.degree. arc to change the orientation of the eccentric axes between the rotor and the internal gear such that, in either direction of rotation, the eccentric collar is disposed in either of its two extreme positions so that the pump has a common inlet and outlet regardless of the direction of rotation of the pump shaft. The movement of the eccentric collar member through the 180.degree. arc has heretofore been dependent upon internal friction within the pump such as friction between the drive shaft and the rotatable face plate positively engaging the eccentric collar, such as is shown in U.S. Pat. No. 3,165,066, or between the outer circular surface of the rotor and the internal cylindrical surface of the eccentric member as disclosed in previously-mentioned U.S. Pat. No. 3,273,501. An indexing pin limits the movement of the eccentric member of 180.degree.. Thus, continuous rotation of the rotor as driven by the internal gear and the drive shaft causes continuous friction to maintain the collar member in the extreme eccentric position. However, in either instance, this continuous friction also causes wear between the parts such that in the first instance, the frictionally engaging parts tend to wear out quite readily and in the second instance, over a period of time, the friction between the eccentric member and the stationary face plate covering the rotor will be greater than the friction between the eccentric member and the rotor, resulting in the eccentric member not always being responsive to a reversal in the direction of rotation of the rotor to change its orientation, resulting in the pump not circulating the lubrication and thus causing damage to the machinery being lubricated.